Capacitance type force sensors

ABSTRACT

Capacitance element electrodes (E 1  to E 5 ) and a grounded reference electrode (E 0 ) are formed on a substrate ( 20 ). A displacement electrode ( 40 ) that is Z-axially displaced in accordance with a Z-axial movement of a detective member ( 30 ) externally operated, is disposed so as to be opposed to the above electrodes (E 0  to E 5 ). The displacement electrode ( 40 ) cooperates with the reference electrode (E 0 ) and the capacitance element electrodes (E 1  to E 5 ) to form capacitance elements (C 0  to C 5 ), respectively. Each of the capacitance elements (C 1  to C 5 ) is connected to the capacitance element (C 0 ) in series in relation to an externally input signal. Changes in the capacitance values of the capacitance elements (C 1  to C 5 ) when the detective member ( 30 ) is moved, is detected by a signal processing circuit having hysteretic characteristics. Thereby, the displacement of the detective member ( 30 ) is detected.

TECHNICAL FIELD

The present invention relates to a capacitance type sensor suitably usedfor inputting operations in multidimensional directions.

BACKGROUND ART

A capacitance type sensor is used as a device for converting theintensity and direction of a force applied by an operator, into anelectric signal. For example, as an input device for a game machine usedis a device incorporated as a capacitance type force sensor, so-calledjoy stick, for inputting operations in multidimensional directions.

Using the capacitance type sensor, an operation quantity with apredetermined dynamic range can be input as the intensity of a forceapplied by the operator. Such a sensor may be used in the form of atwo-dimensional or three-dimensional force sensor capable of detectingeach directional component divided from the applied force. Inparticular, a capacitance type force sensor in which a capacitanceelement is made up of two electrodes and a force is detected on thebasis of a change in the capacitance value due to a change in theinterval between the electrodes, has a merit that a cost reduction canbe intended by simplifying the construction. Therefore, sensors of thistype have been put in practical use in various fields.

A capacitance type sensor is known that includes a pair of fixedelectrodes for detecting opposite directional componential forces, and adisplacement electrode disposed so as to be opposed to the pair of fixedelectrodes. The capacitance type sensor detects an externally appliedforce on the basis of changes in the capacitance values of a capacitanceelement formed between one fixed electrode and the displacementelectrode and a capacitance element formed between the other fixedelectrode and the displacement electrode. The pair of fixed electrodesare supplied with signals, respectively. The signals are delayed on thebasis of changes in the capacitance values of the respective capacitanceelements, and then read by an exclusive OR circuit or the like to derivean output signal.

In the sensitivity characteristic of the above capacitance type sensor,however, each dimensional componential force may not sufficiently bedetected. In addition, when the signals to be input to the respectivefixed electrodes contain noises, the sensor may erroneously operatebecause an erroneous output signal is detected.

Therefore, a principal object of the present invention is to provide acapacitance type sensor superior in sensitivity characteristic and hardto be influenced by noise.

DISCLOSURE OF THE INVENTION

A capacitance type sensor of the present invention is characterized inthat the sensor comprises a conductive member; a capacitance elementelectrode cooperating with the conductive member to form a firstcapacitance element; and a reference electrode electrically connected tothe conductive member and kept at a ground potential or another fixedpotential; the sensor can detect an externally applied force on thebasis of detection of a change in the capacitance value of the firstcapacitance element by utilizing a signal input to the first electrode;and the sensor comprises two capacitance element electrodes in a pair,and output signals corresponding to signals input to a circuit includingone of the capacitance element electrodes and a circuit including theother of the capacitance element electrodes, respectively, are detectedby a signal processing circuit having hysteretic characteristics.

In this feature of the present invention, because a threshold value foran input signal increasing and a threshold value for the input signaldecreasing are different from each other in the signal processingcircuit having the hysteretic characteristics, a change in an outputsignal corresponding to a change in the capacitance value of the firstcapacitance element is wider. Thus, the sensitivity characteristic ofthe sensor is improved in comparison with a case wherein the outputsignal is detected by a signal processing circuit having no hystereticcharacteristics.

In addition, even when an input signal contains noise, because thethreshold value for the input signal increasing and the threshold valuefor the input signal decreasing are different from each other, it issuppressed to detect an erroneous output signal. Thus, an erroneousoperation of the sensor under the influence of the noise can beprevented.

In the capacitance type sensor of the present invention, a secondcapacitance element may be formed between the reference electrode andthe conductive member.

In this feature of the present invention, the conductive member used incommon to form the first and second capacitance elements is electricallyconnected to the reference electrode being kept at the ground or otherfixed potential, not by direct contact but by capacitance coupling.Thus, the withstand voltage characteristic of the sensor is improved andthe sensor is scarcely broken by a spark current flowing, and inaddition, inconvenience such as badness in electrical connection can beprevented. Thus, a highly reliable capacitance type sensor can beobtained. In addition to that, because the first and second capacitanceelements are connected in series, there is no need of separatelyproviding wiring for keeping the conductive member at the ground orother fixed potential if wiring is provided only on a member such as asubstrate supporting the capacitance element electrode and the referenceelectrode. Thus, a capacitance type sensor simple in construction can bemanufactured in a small number of manufacturing steps.

A capacitance type sensor of the present invention is characterized inthat the sensor comprises a substrate that provides an XY plane of anXYZ three-dimensional coordinate system defined; a detective memberbeing opposed to the substrate; a conductive member disposed between thesubstrate and the detective member so as to be Z-axially displaceable inaccordance with Z-axial displacement of the detective member; acapacitance element electrode formed on the substrate to cooperate withthe conductive member to form a first capacitance element; and areference electrode formed on the substrate to cooperate with theconductive member to form a second capacitance element, and kept at aground potential or another fixed potential; the first and secondcapacitance elements are connected in series in relation to a signalinput to the capacitance element electrode, and displacement of thedetective member can be detected on the basis of detection of a changein the capacitance value of the first capacitance element caused by achange in the interval between the conductive member and the capacitanceelement electrode; and the sensor comprises two capacitance elementelectrodes in a pair, and output signals corresponding to signals inputto a circuit including one of the capacitance element electrodes and acircuit including the other of the capacitance element electrodes,respectively, are detected by a signal processing circuit havinghysteretic characteristics.

In this feature of the present invention, like claim 1, because anoutput signal is detected by the signal processing circuit having thehysteretic characteristics, the sensitivity characteristic of the sensoris improved in comparison with a case wherein the output signal isdetected by a signal processing circuit having no hystereticcharacteristics. In addition, like claim 2, a highly reliablecapacitance type sensor can be obtained.

In the capacitance type sensor of the present invention, the capacitanceelement electrode may include a pair of first capacitance elementelectrodes disposed symmetrically with respect to a Y axis, a pair ofsecond capacitance element electrodes disposed symmetrically withrespect to an X axis, and a third capacitance element electrode disposednear an origin.

In this feature of the present invention, the sensor can separatelydetect X-axial, Y-axial, and Z-axial components of an external forcereceived by the detective member. The third capacitance elementelectrodes may not be used for detecting Z-axial components, and may beused for operation for determination of an input.

In the capacitance type sensor of the present invention, a thresholdvalue of the signal processing circuit for an input signal increasingmay be higher than a threshold value of the signal processing circuitfor the input signal decreasing. In the capacitance type sensor of thepresent invention, a Schmitt trigger type logic element that performsone of an exclusive OR operation, an OR operation, an AND operation, anda NAND operation, may be utilized in the signal processing circuit. Inthe capacitance type sensor of the present invention, a Schmitt triggertype buffer element may be utilized in the signal processing circuit. Inthe capacitance type sensor of the present invention, a Schmitt triggertype inverter element may be utilized in the signal processing circuit.In the capacitance type sensor of the present invention, a hysteresiscomparator may be utilized in the signal processing circuit. In thisfeature of the present invention, an output signal can be accuratelydetected. Further, the detection accuracy or detection sensitivity canbe controlled according to need.

In the capacitance type sensor of the present invention, signalsdifferent from each other in phase may be supplied to the circuitincluding one of the capacitance element electrodes and the circuitincluding the other of the capacitance element electrodes. In thisfeature of the present invention, displacement of the detective membercan be detected irrespective of whether or not the circuit including oneof the capacitance element electrodes and the circuit including theother of the capacitance element electrodes have the same time constant.

In the capacitance type sensor of the present invention, a CR circuitincluding one of the capacitance element electrodes and another CRcircuit including the other of the capacitance element electrodes may bedifferent from each other in time constant. In this feature of thepresent invention, because the phase shift between signals by passingthrough the circuits can be wide, the accuracy of detection ofdisplacement of the detective member can be improved.

In the capacitance type sensor of the present invention, the signal maybe a signal in which a high level and a low level are periodicallyrepeated, and the sensor may further comprise a control element having afunction of discharging the first capacitance element when the signal isat the low level. In the capacitance type sensor of the presentinvention, an open collector type inverter element may be used as thecontrol element.

In this feature of the present invention, electric charges are releasedfrom the capacitance element at a moment by the control element such asan open collector type inverter element. Thus, charging can beefficiently performed; the density of waveforms of the signal can beincreased; and the sensitivity of the signal processing circuit can beimproved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view of a capacitance type sensoraccording to an embodiment of the present invention;

FIG. 2 is an upper view of a detective member of the capacitance typesensor of FIG. 1;

FIG. 3 is a view showing an arrangement of a plurality of electrodesformed on a substrate of the capacitance type sensor of FIG. 1;

FIG. 4 is a circuit diagram equivalent to the construction of thecapacitance type sensor shown in FIG. 1;

FIG. 5 is an explanatory diagram for explaining a method for deriving anoutput signal from a periodic signal being input to the capacitance typesensor shown in FIG. 1;

FIG. 6 is a schematic side sectional view when an operation in theX-axial positive direction is applied to the detective member of thecapacitance type sensor shown in FIG. 1;

FIG. 7 is a circuit diagram showing a signal processing circuit of thecapacitance type sensor shown in FIG. 1;

FIG. 8 is a circuit diagram equivalent to the signal processing circuitof the capacitance type sensor shown in FIG. 7;

FIG. 9 is a circuit diagram equivalent to the signal processing circuitof the capacitance type sensor shown in FIG. 7;

FIG. 10 are circuit diagrams showing signal processing circuits forX-axial component of the capacitance type sensor shown in FIG. 1;

FIG. 11 is a circuit diagram showing a signal processing circuit forcomparison with a signal processing circuit shown in FIG. 10;

FIG. 12 is a chart showing waveforms of periodic signals at terminalsand nodes of the signal processing circuit shown in FIG. 1;

FIG. 13 is a chart showing a relation between an input voltagecontaining noise, and an output signal;

FIG. 14 is a view showing an arrangement of a plurality of electrodesformed on the substrate of the capacitance type sensor of FIG. 1,according to a first modification;

FIG. 15 is a circuit diagram showing a signal processing circuit forX-axial component of the capacitance type sensor shown in FIG. 1,according to the first modification;

FIG. 16 is a circuit diagram showing a signal processing circuit forX-axial component of the capacitance type sensor shown in FIG. 1,according to a second modification;

FIG. 17 is a chart showing waveforms of periodic signals at a terminaland nodes of a signal processing circuit shown in FIG. 1 and the signalprocessing circuit shown in FIG. 16;

FIG. 18 is a circuit diagram showing a signal processing circuit forX-axial component of the capacitance type sensor shown in FIG. 1,according to a third modification;

FIG. 19 is a circuit diagram showing a signal processing circuit forX-axial component of the capacitance type sensor shown in FIG. 1,according to a fourth modification;

FIG. 20 is a circuit diagram showing a signal processing circuit forX-axial component of the capacitance type sensor shown in FIG. 1,according to a fifth modification;

FIG. 21 is a circuit diagram showing a signal processing circuit forX-axial component of the capacitance type sensor shown in FIG. 1,according to a sixth modification; and

FIG. 22 is a circuit diagram showing a signal processing circuit forX-axial component of the capacitance type sensor shown in FIG. 1,according to a seventh modification.

BEST FORM FOR CARRYING OUT THE INVENTION

Hereinafter, a preferred embodiment of the present invention will bedescribed with reference to drawings. In the embodiment as will bedescribed below, a capacitance type sensor of the present invention isused as a force sensor.

FIG. 1 is a schematic sectional view of a capacitance type sensoraccording to an embodiment of the present invention. FIG. 2 is an upperview of a detective member of the capacitance type sensor of FIG. 1.FIG. 3 is a view showing an arrangement of a plurality of electrodesformed on a substrate of the capacitance type sensor of FIG. 1.

The capacitance type sensor 10 includes a substrate 20; a detectivemember 30 as an operation member to which a force is externally appliedby operation by a human or the like; a displacement electrode 40;capacitance element electrodes E1 to E5 and a reference electrode E0 asa common electrode, formed on the substrate 20; an insulating film 50formed in close contact with the capacitance element electrodes E1 to E5and the reference electrode E0 to cover the corresponding part of theupper surface of the substrate 20; and a supporting member 60 forsupporting and fixing the detective member 30 and the displacementelectrode 40 to the substrate 20.

For convenience of explanation, an XYZ three-dimensional coordinatesystem is defined as shown in the drawings, and the arrangement of theabove components will be explained with reference to the coordinatesystem. That is, in FIG. 1, the origin O is set on the substrate 20 atthe position opposite to the center of the displacement electrode 40;the X-axis is set so as to extend horizontally rightward; the Z-axis isset so as to extend vertically upward; and the Y-axis is set so as toextend backward perpendicularly to FIG. 1. The upper face of thesubstrate 20 is on an XY-plane. The Z-axis extends through therespective centers of the capacitance element electrode E5 on thesubstrate 20, the detective member 30, and the displacement electrode40.

The substrate 20 is a general printed circuit board for an electroniccircuit. In this embodiment, a glass epoxy board is used. In amodification, a filmy substrate such as a polyimide film may be used asthe substrate 20. In the modification, however, because such a filmysubstrate may be too flexible, it is preferably disposed on asufficiently rigid supporting board.

The detective member 30 is made up of a small-diameter upper stepportion 31 as a force-receiving portion; and a large-diameter lower stepportion 32 formed on the lower end of the upper step portion 31. Thewhole of the detective member 30 is formed into a disk shape. Thediameter of the upper step portion 31 is substantially equal to orsomewhat smaller than the diameter of the circle determined byconnecting the outer circumferential curves of the capacitance elementelectrodes E1 to E4, while the diameter of the lower step portion 32 issubstantially equal to the outer diameter of the reference electrode E0.In order to improve the operability, a resin cap may be put on thedetective member 30.

On the upper face of the upper step portion 31 of the detective member30, as shown in FIG. 2, indicators corresponding to the respectiveoperation directions, i.e., movement directions of a cursor, areprovided so as to correspond to the positive and negative directions ofthe X- and Y-axes, that is, to the respective capacitance elementelectrodes E1 to E4.

The displacement electrode 40 is made of conductive rubber. Thedisplacement electrode 40 is formed into a disk shape having itsdiameter equal to the diameter of the lower step portion 32 of thedetective member 30. The displacement electrode 40 is adhered to thelower face of the detective member 30. In the lower face of thedisplacement electrode 40, a circular recess open downward is formedconcentrically with the displacement electrode 40. On the bottom of therecess, a circular, downward swelling is formed concentrically with thedisplacement electrode 40. A protrusion 45 is formed at the center ofthe swelling, i.e., the center of the displacement electrode 40. Thus,the displacement electrode 40 is made up of a displacement portion 41,as the swelling on the bottom of the recess formed in the lower portionof the displacement electrode 40, that is displaced attendant upon thedisplacement of the detective member 30; a fixed portion 43 being at theoutermost position, as the portion other than the recess formed in thelower portion of the displacement electrode 40; and an interconnectingportion 42, as the portion other than the swelling of the bottom of therecess formed in the lower portion of the displacement electrode 40,interconnecting the displacement and fixed portions 41 and 43. In amodification, such a protrusion 45 may not be provided. In anothermodification, the displacement electrode 40 may be made of metal havingelectrical conductivity.

In this embodiment, the protrusion 45 is formed at the center of thedisplacement electrode 40, as described above. Thus, when a force isapplied to the detective member 30, the displacement electrode 40 canincline with the protrusion 45 serving as a fulcrum. As well as thedetective member 30, the displacement electrode 40 is supported andfixed by the supporting member 60 so that the lower faces of the fixedportion 43 and protrusion 45 can be in close contact with the insulatingfilm 50 formed on the substrate 20. The protrusion 45 has a function ofan elastic material for receiving a force in a certain extent andbringing the displacement electrode 40 near to the substrate 20 when thedetective member 30 is strongly, Z-axially depressed.

On the substrate 20, as shown in FIG. 3, there are formed a circularcapacitance element electrode E5 having its center at the origin O;fan-shaped capacitance element electrodes E1 to E4 disposed outside thecapacitance element electrode E5; and a ring-shaped reference electrodeE0 disposed outside the capacitance element electrodes E1 to E4 so thatthe center of the reference electrode E0 is at the origin O. Thecapacitance element electrodes E1 and E2 in a pair are disposed so as tobe X-axially distant from each other and symmetrical with respect to theY-axis. On the other hand, the capacitance element electrodes E3 and E4in a pair are disposed so as to be Y-axially distant from each other andsymmetrical with respect to the X-axis. In a modification, the referenceelectrode E0 may be formed between the capacitance element electrode E5and the capacitance element electrodes E1 to E4. In anothermodification, the capacitance element electrode E5 may be omitted andthere may be formed a circular reference electrode E0 having its centerat the origin O. In the latter modification, however, any Z-axialcomponent cannot be detected.

In this embodiment, the capacitance element electrode E1 is disposed soas to correspond to the X-axial positive direction while the capacitanceelement electrode E2 is disposed so as to correspond to the X-axialnegative direction. Thus, they are used for detecting the X-axialcomponent of an external force. On the other hand, the capacitanceelement electrode E3 is disposed so as to correspond to the Y-axialpositive direction while the capacitance element electrode E4 isdisposed so as to correspond to the Y-axial negative direction. Thus,they are used for detecting the Y-axial component of an external force.Further, the capacitance element electrode E5 is disposed on the originO and it is used for detecting the Z-axial component of an externalforce.

The reference electrode E0 and the capacitance element electrodes E1 toE5 are connected to terminals T0 to T5, as shown in FIG. 4, usingthrough-holes or the like, respectively. They are connected to anexternal electronic circuit through the terminals T0 to T5. In thisembodiment, the reference electrode E0 is grounded through the terminalT0.

The insulating film 50 is formed in close contact with the capacitanceelement electrodes E1 to E5 and reference electrode E0 on the substrate20 to cover the corresponding part of the upper face of the substrate20. Therefore, the capacitance element electrodes E1 to E5 and referenceelectrode E0, which are made of copper or the like, are never exposed toair. Thus, the insulating film 50 has a function of preventing them frombeing oxidized. In addition, because the insulating film 50 is formed,the displacement electrode 40 is never brought into direct contact withthe capacitance element electrodes E1 to E5 and reference electrode E0.

Thus, each of the capacitance element electrodes E1 to E5 and referenceelectrode E0 cooperates with the displacement electrode 40 to form acapacitance element between them. More specifically, the capacitanceelement electrodes E1 to E5 cooperate with the displacement portion 41of the displacement electrode 40 to form capacitance elements C1 to C5,respectively. The reference electrode E0 cooperates with the fixedportion 43 of the displacement electrode 40 to form a capacitanceelement C0.

Next, an operation of the capacitance type sensor 10 according to thisembodiment constructed as described above will be described withreference to drawings. FIG. 4 is a circuit diagram equivalent to theconstruction of the capacitance type sensor shown in FIG. 1. FIG. 5 isan explanatory diagram for explaining a method for deriving an outputsignal from a periodic signal being input to the capacitance type sensorshown in FIG. 1. FIG. 6 is a schematic side sectional view when anoperation in the X-axial positive direction is applied to the detectivemember of the capacitance type sensor shown in FIG. 1.

First, a circuit construction equivalent to the construction of thecapacitance type sensor 10 will be described with reference to FIG. 4.The capacitance element electrodes E1 to E5 and reference electrode E0formed on the substrate 20 are opposed to the displacement electrode 40.The capacitance elements C0 to C5 are formed between the deformabledisplacement electrode 40 as a common electrode and the fixed referenceelectrode E0 and capacitance element electrodes E1 to E5, respectively.The capacitance elements C1 to C5 are variable capacitance elementswhose capacitance values change due to the deformation of thedisplacement electrode 40.

The capacitance values of the capacitance elements C0 to C5 can bemeasured independently of one another as the capacitance values betweenthe displacement electrode 40 and the respective terminals T0 to T5connected to the reference electrode E0 and capacitance elementelectrodes E1 to E5. The reference electrode E0 is grounded through theterminal T0. Thus, the displacement electrode 40 as a common electrodeof the capacitance elements C1 to C5 is considered to be groundedthrough the capacitance element C0 and the terminal T0. That is, thecapacitance element C0 makes capacitive coupling between thedisplacement electrode 40 and the terminal T0.

Next, a deriving method of an output signal indicating the intensity anddirection of an external force applied to the detective member 30, froma change in the capacitance value of each of the capacitance elements C1to C5, will be described with reference to FIG. 5. In FIG. 5, outputsignals V_(x), V_(y), and V_(z) indicate the intensities and directionsof the X-axial, Y-axial, and Z-axial components of an external force,respectively. To indicate that any of the output signals V_(x), V_(y),and V_(z) is output from a Schmitt trigger type logic element includedin a signal processing circuit having hysteretic characteristics, thesymbol of each logic element is given therein a mark symbolizing thehysteretic characteristics.

A capacitance element C6 as shown in FIG. 5 is formed on the lower faceof the substrate 20 so as to always keep a certain capacitance value.One electrode constituting the capacitance element C6 is connected to aC/V converter for deriving the output signal V_(z), and the otherelectrode is grounded. The capacitance element C6 is used in cooperationwith the capacitance element C5 to derive the output signal V_(z) forthe Z-axial component of an external force. In a modification, the inputcapacitance of an IC may be used as the capacitance element C6. Inanother modification, such a capacitance element C6 may be formed by anot-shown sixth electrode E6 and a portion of the displacement electrode40 hard to be deformed.

In this embodiment, for deriving the output signals V_(x), V_(y), andV_(z), a periodic signal such as a clock signal is always being input toeach of the terminals T1 to T6. For example, with respect to theperiodic signal being input to the terminal T1, two capacitance elementsC1 and C0 are connected in series. Likewise, two capacitance elements C2and C0 are connected in series with respect to the periodic signal beinginput to the terminal T2; two capacitance elements C3 and C0 areconnected in series with respect to the periodic signal being input tothe terminal T3; two capacitance elements C4 and C0 are connected inseries with respect to the periodic signal being input to the terminalT4; and two capacitance elements C5 and C0 are connected in series withrespect to the periodic signal being input to the terminal T5.

When the detective member 30 receives an external force to be deformedin a state wherein the periodic signals are being input to the terminalsT1 to T6, the displacement electrode 40 is Z-axially deformedaccordingly. The interval between the electrodes of each of thecapacitance elements C1 to C5 then changes and thereby the capacitancevalues of the respective capacitance elements C1 to C5 change. As aresult, phase shifts occur in the periodic signals being input to theterminals T1 to T6. Using the phase shifts thus occurring in the cyclicsignals, the output signals V_(x), V_(y), and V_(z) can be obtained thatindicate the displacement of the detective member 30, that is, theX-axial, Y-axial, and Z-axial intensities and directions of the externalforce received by the detective member 30.

More specifically, when periodic signals are being input to theterminals T1 to T6, a periodic signal A is being input to the terminalsT1, T3, and T5, and another periodic signal B having the same cycle asthe periodic signal A and different in phase from the periodic signal Ais being input to the terminals T2, T4, and T6. In this case, when thedetective member 30 receives an external force and the capacitancevalues of the respective capacitance elements C1 to C5 change, differentquantities of phase shifts occur in the periodic signal A or B beinginput to the terminals T1 to T5. At this time, no phase shift occurs inthe periodic signal B being input to the terminal T6 because thecapacitance value of the capacitance element C6 dose not change.

When the external force has its X-axial component, the capacitance valueof the capacitance element C1 changes and it causes a phase shift in theperiodic signal A being input to the terminal T1. In addition, thecapacitance value of the capacitance element C2 changes and it causes aphase shift also in the periodic signal B being input to the terminalT2. The changes in the capacitance values of the capacitance elements C1and C2 correspond to the X-axial positive and negative components of theexternal force, respectively. Therefore, the phase shift in the periodicsignal A being input to the terminal T1 is in the reverse direction tothe phase shift in the periodic signal B being input to the terminal T2.The respective phase shifts in the periodic signals A and B being inputto the terminals T1 and T2 are read by an exclusive OR circuit to derivean output signal V_(x). The sign of the output signal V_(x) indicateswhether the X-axial component of the external force is in the positiveor negative direction. The absolute value of the output signal V_(x)indicates the intensity of the X-axial component.

When the external force has its Y-axial component, the capacitance valueof the capacitance element C3 changes and it causes a phase shift in theperiodic signal A being input to the terminal T3. In addition, thecapacitance value of the capacitance element C4 changes and it causes aphase shift also in the periodic signal B being input to the terminalT4. The changes in the capacitance values of the capacitance elements C3and C4 correspond to the Y-axial positive and negative components of theexternal force, respectively. Therefore, the phase shift in the periodicsignal A being input to the terminal T3 is in the reverse direction tothe phase shift in the periodic signal B being input to the terminal T4.The respective phase shifts in the periodic signals A and B being inputto the terminals T3 and T4 are read by an exclusive OR circuit to derivean output signal V_(y). The sign of the output signal V_(y) indicateswhether the Y-axial component of the external force is in the positiveor negative direction. The absolute value of the output signal V_(y)indicates the intensity of the Y-axial component.

When the external force has its Z-axial component, the capacitance valueof the capacitance element C5 changes and it causes a phase shift in theperiodic signal A being input to the terminal T5. In this case, no phaseshift occurs in the periodic signal B being input to the terminal T6because the capacitance value of the capacitance element C6 is keptconstant. Thus, the phase shift occurs only in the periodic signal Abeing input to the terminal T5. The phase shift in the periodic signal Ais read by an exclusive OR circuit to derive an output signal V_(z). Thesign of the output signal V_(z) indicates whether the Z-axial componentof the external force is in the positive or negative direction. Theabsolute value of the output signal V_(z) indicates the intensity of theZ-axial component.

Incidentally, when the external force has its X-axial or Y-axialcomponent, in accordance with the manner of application of the force tothe detective member 30, the following cases are thinkable. For example,as for the X-axial directions, there may be a case wherein the X-axialpositive and negative parts of the displacement portion 41 are deformedwith the protrusion 45 serving as a fulcrum, not in the verticallyreverse directions to each other but so that both the X-axial positiveand negative parts are deformed downward in different quantities. Inthis case, although phase shifts in the same direction occur in theperiodic signals A and B being input to the terminals T1 and T2, anoutput signal V_(x) can be derived by the exclusive OR circuit readingthe phase shifts, like the above-described case. The same applies to thecase of deriving an output signal V_(y) with respect to the Y-axis.

Next, a case will be described wherein, in a state wherein no force hasbeen applied to the detective member 30 shown in FIG. 1, as shown inFIG. 6, an operation in the X-axial positive direction is applied to thedetective member 30, that is, a force in the Z-axial negative directionis applied to the detective member 30 so that the indicator formed onthe upper step portion 31 of the detective member 30 to correspond tothe X-axial positive direction may be depressed toward the substrate 20.

By depressing the part of the detective member 30 corresponding to theX-axial positive direction, the interconnecting portion 42 of thedisplacement electrode 40 is elastically deformed and bent. The X-axialpositive part of the displacement portion 41 thereby moves downward. Ina short time, the X-axial positive part of the displacement portion 41reaches the position at which the lower surface of the displacementportion 41 is in contact with the insulating film 50. At this time, theX-axial positive and negative parts of the displacement portion 41 movein the vertically reverse directions to each other, with the protrusion45 serving as a fulcrum. Therefore, when the X-axial positive part ofthe displacement portion 41 moves downward, the X-axial negative part ofthe displacement portion 41 moves upward, with the protrusion 45 servingas a fulcrum.

In addition, a portion of the Y-axial positive part of the displacementportion 41 near the X-axial positive part somewhat moves downward, whilea portion of the Y-axial positive part near the X-axial negative partsomewhat moves upward. Likewise, a portion of the Y-axial negative partnear the X-axial positive part somewhat moves downward, while a portionof the Y-axial negative part near the X-axial negative part somewhatmoves upward. Further, at this time, the protrusion 45 formed at thecenter of the displacement portion 41 on the Z-axis is crushed andelastically deformed.

Thus, the interval between the X-axial positive part of the displacementportion 41 and the capacitance element electrode E1 decreases, while theinterval between the X-axial negative part of the displacement portion41 and the capacitance element electrode E2 increases. The intervalbetween the Y-axial positive part of the displacement portion 41 and thecapacitance element electrode E3 and the interval between the Y-axialnegative part of the displacement portion 41 and the capacitance elementelectrode E4 are considered to be unchanged when they are averaged.Actually, as described above, the portions of the Y-axial positive andnegative parts of the displacement portion 41 near the X-axial positivepart somewhat move downward and the portions of the Y-axial positive andnegative parts near the X-axial negative part somewhat move upward. Onthe whole, however, the respective intervals between the Y-axialpositive and negative parts of the displacement portion 41 and thecapacitance element electrodes E3 and E4 can be considered to beunchanged. In addition, even if the interval between the Y-axialpositive part of the displacement portion 41 and the capacitance elementelectrode E3 and the interval between the Y-axial negative part of thedisplacement portion 41 and the capacitance element electrode E4partially change, the quantities of changes in the capacitance values ofthe capacitance element C3 formed between the Y-axial positive part ofthe displacement portion 41 and the capacitance element electrode E3,and the capacitance element C4 formed between the Y-axial negative partof the displacement portion 41 and the capacitance element electrode E4are considered to be equal to each other because of their mechanicalsymmetry. Thus, there appears no output by the operation principle. Onthe other hand, the interval between the central part of thedisplacement portion 41 and the capacitance element electrode E5decreases.

Thus, of the capacitance elements C1 to C5, changes occur only in thecapacitance values of the capacitance elements C1, C2, and C5 that havesuffered changes in the intervals between the capacitance elementelectrodes and the displacement electrode 40. In general, thecapacitance value of a capacitance element is in inverse proportion tothe interval between the electrodes forming the capacitance element.Thus, the capacitance value of the capacitance element C1 increaseswhile the capacitance value of the capacitance element C2 decreases. Asa result, the relation in magnitude among the capacitance values of thecapacitance elements C1 to C4 is as follows:

C2 smaller than C3 equal to C4 smaller than Cl. The capacitance value ofthe capacitance element C5 increases from its original value.

At this time, phase shifts occur in the periodic signals A and B beinginput to the terminals T1 and T2. The phase shifts are read to derive anoutput signal V_(x). Likewise, a phase shift occurs in the periodicsignal A being input to the terminal T5 and the phase shift is read,actually, together with the phase of the periodic signal B being inputto the terminal T6, to derive an output signal V_(y).

Next, a signal processing circuit for deriving output signals V_(x),V_(y), and V_(z) from the periodic signals A and B being input to theterminals T1 to T6 will be described with reference to FIG. 7. FIG. 7 isa circuit diagram showing a signal processing circuit of the capacitancetype sensor shown in FIG. 1. FIGS. 8 and 9 are circuit diagrams showingsignal processing circuits equivalent to the signal processing circuitof the capacitance type sensor shown in FIG. 7.

As described above, periodic signals of a predetermined frequency arebeing input to the terminals T1 to T6 from a not-shown AC signaloscillator. Inverter elements I1 to I6 and resistance elements R1 to R6are connected to the terminals T1 to T6, respectively. The inverterelements I1 to I6 and the resistance elements R1 to R6 are connected inthis order from the terminals T1 to T6, respectively. EX-OR elements 101to 103 as logic elements of Schmitt trigger type exclusive OR circuitsare connected to the output terminals of the resistance elements R1 andR2, the output terminals of the resistance elements R3 and R4, and theoutput terminals of the resistance elements R5 and R6, respectively. Theoutput terminals of the EX-OR elements 101 to 103 are connected toterminals T11 to T13, respectively. The output terminals of theresistance elements R1 to R5 are connected to the capacitance elementelectrodes E1 to E5 to form the respective capacitance elements C1 to C5in cooperation with the displacement electrode 40. The displacementelectrode 40 is grounded through the capacitance element C0.

In a modification, the signal processing circuit using the EX-ORelements 101 to 103 as logic elements of Schmitt trigger type exclusiveOR circuits, shown in FIG. 7, can be changed into a signal processingcircuit using Schmitt trigger type buffer elements 111 to 116, as shownin FIG. 8, or a signal processing circuit using Schmitt trigger typeinverter elements 121 to 126, as shown in FIG. 9. These signalprocessing circuits are equivalent to one another.

Hereinafter, by way of example, a deriving method of an output signalV_(x) for X-axial component will be described with reference to FIG. 10.Because deriving methods of an output signal V_(y) for Y-axial componentand an output signal V_(z) for Z-axial component are the same as thederiving method of the output signal V_(x) for X-axial component, thedescription of the deriving methods of the output signal V_(y) forY-axial component and the output signal V_(z) for Z-axial component isomitted. Either of FIGS. 10( a) and 10(b) is a circuit diagram, as partof FIG. 8, showing a signal processing circuit for X-axial component inthe capacitance type sensor shown in FIG. 1. Because the circuitdiagrams showing the signal processing circuits of FIGS. 7 to 9 areequivalent to one another, the deriving method of the output signalV_(x) for X-axial component will be described below on the basis of FIG.8.

In this signal processing circuit, the capacitance element C1 and theresistance element R1 forms a CR delay circuit, and the capacitanceelement C2 and the resistance element R2 forms another CR delay circuit.Periodic signals, as rectangular wave signals, being input to theterminals T1 and T2 suffer predetermined delays due to the respective CRdelay circuits; they pass through the Schmitt trigger type bufferelements 111 and 112; and then they meet each other in an EX-OR element131. Because identical elements are used as the inverter elements I1 andI2, the signals through the different paths can be compared under thesame conditions. The inverter elements I1 and I2 are elements to producedriving powers sufficient for driving the respective CR delay circuits,and they are logically meaningless elements. Therefore, if the terminalsT1 and T2 can be supplied with signals each having sufficient drivingability, the inverter elements I1 and I2 may be omitted. In FIG. 10( b),there have been omitted the inverter elements I1 and I2 that areincluded in the signal processing circuit of FIG. 10( a). Thus, thecircuit of FIG. 10( b) is considered to be quite equivalent to thecircuit of FIG. 10( a).

Next, a signal processing circuit of the capacitance type sensoraccording to this embodiment will be described with reference todrawings. FIG. 11 is a circuit diagram showing a signal processingcircuit for comparison with a signal processing circuit shown in FIG.10. FIG. 12 is a chart showing waveforms of periodic signals atterminals and nodes of the signal processing circuits shown in FIGS. 10and 11.

As for the signal processing circuit shown in FIG. 10( b), the waveformsof periodic signals at terminals and nodes when the periodic signals arebeing input to the respective terminals T1 and T2 will be described withbeing compared with the waveforms of the periodic signals at terminalsand nodes when a signal processing circuit not having hystereticcharacteristics, as shown in FIG. 11, is used as a signal processingcircuit of the capacitance type sensor according to this embodiment.

In the signal processing circuit of FIG. 10( b), the periodic signalsbeing input to the respective terminals T1 and T2 suffer predetermineddelays by passing through the CR delay circuits; they pass through theSchmitt trigger type buffer elements 111 and 112; and then they areinput to the EX-OR element 131. More specifically, a periodic signalf(phi) (corresponding to the above-described periodic signal A andhereinafter referred to as the periodic signal A) is being input to theterminal T1, while a periodic signal f(phi-theta) (corresponding to theabove-described periodic signal B and hereinafter referred to as theperiodic signal B) having the same cycle as the periodic signal f(phi)and different in phase by theta, is being input to the terminal T2. Inthis embodiment, a case will be described wherein the duty ratio of theperiodic signal A is 50% and the periodic signal B is delayed in phasefrom the periodic signal A by a quarter of the cycle of the periodicsignal A. In FIG. 12, (a) and (b) show the waveforms of the periodicsignals A and B being input to the terminals T1 and T2, respectively.

In this embodiment, the periodic signals A and B different in phase, tobe input to the respective terminals T1 and T2, can be generated in themanner that a periodic signal output from a single AC signal oscillatoris divided into two paths; a not-shown CR delay circuit is provided inone of the paths; and thereby the phase of the periodic signal havingpassed through the CR delay circuit is delayed. But, the method forshifting the phase of the periodic signal is not limited to such amethod using a CR delay circuit. Any other method may be used. In amodification, two AC signal oscillators may be used for generatingperiodic signals A and B different in phase, to be input to therespective terminals T1 and T2.

In the signal processing circuit of FIG. 10( b), the periodic signals Aand B being input to the terminals T1 and T2 are delayed by passingthrough the delay circuit constituted by the capacitance element C1 andthe resistance element R1, and the delay circuit constituted by thecapacitance element C2 and the resistance element R2; and then theyreach nodes X11 and X12, respectively. The capacitance values of thecapacitance elements C1 and C2 in a state wherein the detective member30 is receiving no external force, i.e., no operation is applied to thedetective member 30, are the capacitance values based on the intervalsbetween the displacement electrode 40 and the capacitance elementelectrodes E1 and E2 in a state wherein the detective member 30 isreceiving no external force. FIG. 12( c) shows a change in the potentialat the node X11 of the signal processing circuit shown in FIG. 10( b).FIG. 12( d) shows a change in the potential at the node X12 of thesignal processing circuit shown in FIG. 10( b).

In the case that a periodic signal in which “Hi” and “Lo” signals arerepeated is input to the terminal T1, as shown in FIG. 12( c), afterstarting the input of a “Hi” signal, charges are gradually stored in thecapacitance element C1 constituting a CR delay circuit, so that thepotential at the node X11 gradually rises. On the other hand, afterstarting the input of a “Lo” signal, charges are gradually released fromthe capacitance element C1 constituting the CR delay circuit, so thatthe potential at the node X11 gradually lowers. These changes arerepeated. Also in the case that a periodic signal in which “Hi” and “Lo”signals are repeated is input to the terminal T2, as shown in FIG. 12(d), changes similar to those in the potential at the node X11 arerepeated in the potential at the node X12.

The waveforms of the potentials at the nodes X11 and X12 are input tothe Schmitt trigger type buffer elements 111 and 112 to be convertedinto rectangular waves as shown in (e) and (f) of FIG. 12. FIG. 12( e)shows the periodic signal waveform at a node X13 of the signalprocessing circuit shown in FIG. 10( b). FIG. 12( f) shows the periodicsignal waveform at a node X14 of the signal processing circuit shown inFIG. 10( b).

Conversion processing by the Schmitt trigger type buffer elements 111and 112 will be described below in detail. In the Schmitt trigger typebuffer elements 111 and 112, the threshold voltage for the input voltagerising (hereinafter referred to as positive threshold voltage Vp) andthe threshold voltage for the input voltage lowering (hereinafterreferred to as negative threshold voltage Vn) are set so as to bedifferent from each other. Thus, there are set two threshold voltages ofthe positive threshold voltage Vp and the negative threshold voltage Vnlower than the positive threshold voltage Vp.

Therefore, when the rising input voltage becomes higher than thepositive threshold voltage Vp, the output signal is changed over from a“Lo” signal into a “Hi” signal. On the other hand, when the loweringinput voltage becomes lower than the negative threshold voltage Vn, theoutput signal is changed over from a “Hi” signal into a “Lo” signal.

An output signal in the case that the input voltage contains noise willbe described with reference to FIG. 13. FIG. 13 is a chart showing arelation between an input voltage containing noise, and an outputsignal.

First, when the input voltage containing noise rises, as shown in FIG.13, the input voltage once becomes higher than the positive thresholdvoltage Vp at a time Ta. Afterward, the input voltage becomes lower thanthe positive threshold voltage Vp at a time Tb, and then again higherthan the positive threshold voltage Vp at a time Tc. In this case, asdescribed above, the output signal is changed over at the time Ta from a“Lo” signal into a “Hi” signal. Although the input voltage becomes lowerthan the positive threshold voltage Vp at the time Tb, the output signalis not changed over from the “Hi” signal into the next “Lo” signalbecause the input voltage does not become lower than the negativethreshold voltage Vn. Thus, the output signal at the “Hi” levelcontinues at the times Tb and Tc.

On the other hand, when the input voltage containing noise lowers, theinput voltage once becomes lower than the negative threshold voltage Vnat a time Td. Afterward, the input voltage becomes higher than thenegative threshold voltage Vn at a time Te, and then again lower thanthe negative threshold voltage Vn at a time Tf. In this case, asdescribed above, the output signal is changed over at the time Td fromthe “Hi” signal into the next “Lo” signal. Although the input voltagebecomes higher than the negative threshold voltage Vn at the time Te,the output signal is not changed over from the “Lo” signal into the next“Hi” signal because the input voltage does not become higher than thepositive threshold voltage Vp. Thus, the output signal at the “Lo” levelcontinues at the times Te and Tf.

As described above, even in the case that the input voltage variesaround the positive and negative threshold voltages Vp and Vn because ofthe noise contained in the input voltage, it is suppressed to detect anerroneous output signal.

In the case that each of the Schmitt trigger type buffer elements 111and 112 is a CMOS type element and the power supply voltage is Vcc, ingeneral, the positive threshold voltage Vp is in between Vcc/2 and Vcc,and the negative threshold voltage Vn is in between zero and Vcc/2. In ageneral Schmitt trigger type buffer element, when the power supplyvoltage Vcc is 4.5 V, the positive threshold voltage Vp is 2.7 V, andthe negative threshold voltage Vn is 1.6 V. As will be described later,the threshold voltage of a CMOS type logic element is around Vcc/2 ingeneral.

As described above, the rectangular wave at the node X13, as shown inFIG. 12( e), and the rectangular wave at the node X14, as shown in FIG.12( f), are input to the EX-OR element 131. An exclusive OR operation isperformed for those signals, and the result of the operation is outputto the terminal T11. In this case, the output signal Vx output to theterminal T11 is a rectangular wave signal having its duty ratio D1, asshown in FIG. 12( g).

Next, a case will be described wherein an operation in the X-axialpositive direction is applied to the detective member 30, as shown inFIG. 6. In this case, as described above, because a portion of thedetective member 30 corresponding to the X-axial positive direction isdepressed, the portion of the detective member 30 corresponding to theX-axial positive direction is displaced downward and a portion of thedetective member 30 corresponding to the X-axial negative direction isdisplaced upward. Thereby, the capacitance value of the capacitanceelement C1 increases and the capacitance value of the capacitanceelement C2 decreases. This brings about changes in the quantities of thedelays of the periodic signals A and B, which were input to theterminals T1 and T2, by passing through the delay circuit constituted bythe capacitance element C1 and the resistance element R1, and the delaycircuit constituted by the capacitance element C2 and the resistanceelement R2.

In the signal processing circuit of FIG. 10( b), the periodic signals Aand B being input to the respective terminals T1 and T2 are delayed bypassing through the delay circuit constituted by the capacitance elementC1 and the resistance element R1, and the delay circuit constituted bythe capacitance element C2 and the resistance element R2, in a statewherein the capacitance values of the capacitance elements C1 and C2have changed; and then they reach nodes X11′ and X12′, respectively.Here, the nodes at the same positions as the nodes X11 and X12 of thesignal processing circuit shown in FIG. 10( b) are denoted by X11′ andX12′, respectively, in the case that an operation in the X-axialpositive direction is applied to the detective member 30. FIG. 12( h)shows a change in the potential at the node X11′ of the signalprocessing circuit shown in FIG. 10( b). FIG. 12( i) shows a change inthe potential at the node X12′ of the signal processing circuit shown inFIG. 10( b).

In this embodiment, also in the case that the operation in the X-axialpositive direction is applied to the detective member 30, the waveformsof the potentials at the nodes X11′ and X12′ are input to the respectiveSchmitt trigger type buffer elements 111 and 112 to be converted intorectangular waves. The converted rectangular waves are input to theEX-OR element 131. An exclusive OR operation is performed for thosesignals, and the result of the operation is output to the terminal T11.In this case, the output signal Vx output to the terminal T11 is arectangular wave signal having its duty ratio D2, as shown in FIG. 12(j).

Next will be described the waveforms of periodic signals at terminalsand nodes in the case of using, as a signal processing circuit of thecapacitance type sensor 10 according to this embodiment, a signalprocessing circuit having no hysteretic characteristics, that is, asignal processing circuit in which the Schmitt trigger type bufferelements 111 and 112 have been removed from the signal processingcircuit shown in FIG. 10( b).

In the case of the EX-OR element 131 as a CMOS type logic element usedin the signal processing circuit shown in FIG. 11, only one thresholdvoltage is set while two different threshold voltages are set for eachof the Schmitt trigger type buffer elements 111 and 112. When the inputvoltage becomes higher than the threshold voltage, the output signal ischanged over from a “Lo” signal into a “Hi” signal. When the inputvoltage becomes lower than the threshold voltage, the output signal ischanged over from a “Hi” signal into a “Lo” signal. Thereby, the outputsignal is converted into a rectangular wave signal. In the case of aCMOS type logic element, in many cases, the threshold voltage is setaround Vcc/2 when the power supply voltage is Vcc.

In the signal processing circuit shown in FIG. 11, the periodic signalsA and B being input to the respective terminals T1 and T2 are delayed bypassing through the delay circuit constituted by the capacitance elementC1 and the resistance element R1, and the delay circuit constituted bythe capacitance element C2 and the resistance element R2, in a statewherein the detective member 30 is receiving no external force, i.e., nooperation is applied to the detective member 30; and then they reachesnodes X21 and X22, respectively. At this time, the changes in thepotentials at the nodes X21 and X22 of the signal processing circuitshown in FIG. 11 are the same as (c) and (d) of FIG. 12.

The waveforms of the potentials at the nodes X21 and X22 are input tothe EX-OR element 131. After the waveforms of the potentials at thenodes X21 and X22 are converted into rectangular waves as describedabove, an exclusive OR operation is performed for those signals, and theresult of the operation is input to the terminal T11. In this case, theoutput signal Vx output to the terminal T11 is a rectangular wave signalhaving its duty ratio D3, as shown in FIG. 12( k).

Next, a case will be described wherein an operation in the X-axialpositive direction is applied to the detective member 30, as shown inFIG. 6. In this case, like the above-described case, the capacitancevalues of the capacitance elements C1 and C2 change.

In the signal processing circuit shown in FIG. 11, the periodic signalsA and B being input to the respective terminals T1 and T2 are delayed bypassing through the delay circuit constituted by the capacitance elementC1 and the resistance element R1, and the delay circuit constituted bythe capacitance element C2 and the resistance element R2, in a statewherein the capacitance values of the capacitance elements C1 and C2have changed; and then they reach nodes X21′ and X22′, respectively.Here, the nodes at the same positions as the nodes X21 and X22 of thesignal processing circuit shown in FIG. 11 are denoted by X21′ and X22′,respectively, in the case that an operation in the X-axial positivedirection is applied to the detective member 30.

The waveforms at the nodes X11′ and X12′ are input to the EX-OR element131. After the waveforms are converted into rectangular waves, anexclusive OR operation is performed for those signals, and the result ofthe operation is input to the terminal T11. In this case, the outputsignal Vx output to the terminal T11 is a rectangular wave signal havingits duty ratio D4, as shown in FIG. 12( l).

As described above, in the case that a signal processing circuit havinghysteretic characteristics, as shown in FIG. 10( b), is used as a signalprocessing circuit of the capacitance type sensor 10 according to thisembodiment, the duty ratio of the output signal Vx output to theterminal T11 changes from D1 to D2 by applying an operation in theX-axial positive direction to the detective member 30 from a statewherein the detective member 30 is receiving no external force. On theother hand, in the case that a signal processing circuit having nohysteretic characteristics, as shown in FIG. 11, is used, the duty ratioof the output signal Vx output to the terminal T11 changes from D3 to D4by applying an operation in the X-axial positive direction to thedetective member 30 from a state wherein the detective member 30 isreceiving no external force.

The quantity of the change between the duty ratio D1 of the rectangularwave signal of FIG. 12( g) and the duty ratio D2 of the rectangular wavesignal of FIG. 12( j) is larger than the quantity of the change betweenthe duty ratio D3 of the rectangular wave signal of FIG. 12( k) and theduty ratio D4 of the rectangular wave signal of FIG. 12( l). In manycases, the output signal Vx output to the terminal T11 is used afterconverted into an analogue voltage. In the case that the output signalVx is converted into an analogue voltage, the quantities of the changebetween duty ratios of two rectangular wave signals are integrated.Therefore, in the case of using the signal processing circuit havinghysteretic characteristics, as shown in FIG. 10( b), in which thequantity of the change in the duty ratio is large, the sensitivitycharacteristic of the sensor can be improved in comparison with the caseof using the signal processing circuit having no hystereticcharacteristics, as shown in FIG. 11.

As described above, in the capacitance type sensor 10 of thisembodiment, because a signal processing circuit having hystereticcharacteristics is used as a signal processing circuit of the sensor,the positive threshold voltage Vp for the input voltage rising and thenegative threshold voltage Vn for the input voltage lowering aredifferent from each other. The quantity of the change in the duty ratioof the output signal in the case of being detected by the signalprocessing circuit having hysteretic characteristics is larger than thequantity of the change in the duty ratio of the output signal in thecase of being detected by a signal processing circuit having nohysteretic characteristics. Thus, the sensitivity characteristic of thesensor is improved.

In addition, even in the case that a periodic signal to be inputcontains noise, because the threshold voltage for the input voltagerising and the threshold voltage for the input voltage lowering aredifferent from each other, it is suppressed to detect an erroneousoutput signal. Thus, the sensor can be prevented from erroneouslyoperating by the influence of the noise.

Because the displacement electrode 40 used in common to constitute aplurality of capacitance elements C0 to C5 is electrically connected bycapacitance coupling to the reference electrode E0 kept at the groundpotential or another fixed potential, the displacement electrode 40 neednot be in direct contact with the reference electrode E0 for electricalconnection. Thereby, the withstand voltage characteristic of the sensoris improved, and the sensor is scarcely broken by a spark currentflowing. In addition, malfunction such as a defect in electricalconnection can be prevented. Thus, a capacitance type sensor high inreliability can be obtained. In addition, because the capacitanceelements C1 and C0; C2 and C0; . . . ; and C5 and C0 are connected inseries with respect to a periodic signal, wiring need not be providedfor keeping the displacement electrode 40 at the ground potential oranother fixed potential if wiring is provided on the substrate 20supporting the capacitance element electrodes and the referenceelectrode. Therefore, the capacitance type sensor simple in constructioncan be manufactured in a small number of manufacturing steps.

Further, a plurality of capacitance element electrodes E1 to E5 areformed, and the X-axial, Y-axial, and Z-axial components of an externalforce received by the detective member 30 can be detected separatelyfrom one another. Because signals different from each other in phase areinput to each pair of capacitance element electrodes, i.e., E1 and E2;and E3 and E4, the shifts in phase of the signals by passing throughcircuits can be made wide. Further, the signals can be accuratelydetected because a signal processing circuit utilizing logic elements isused.

Next, a first modification of the embodiment of the present inventionwill be described with reference to drawings. FIG. 14 is a view showingan arrangement of a plurality of electrodes formed on a substrate of acapacitance type sensor according to the first modification.

In the capacitance type sensor according to the first modification, theconstitution of the reference electrode E0 on the substrate 20 of thecapacitance type sensor of FIG. 1 has been modified so that referenceelectrodes E01 to E04 are formed as shown in FIG. 14. The otherconstitutions are the same as those of the capacitance type sensor ofFIG. 1, and thus the same references as the capacitance type sensor ofFIG. 1 for the constitutions are used, thereby omitting the descriptionthereof.

On the substrate 20, as shown in FIG. 14, there are formed a circularcapacitance element electrode E5 having its center at the origin O;fan-shaped capacitance element electrodes E1 to E4 disposed outside thecapacitance element electrode E5; and fan-shaped reference electrodesE01 to E04 disposed outside the capacitance element electrodes E1 to E4.In this modification, each pair of capacitance element electrode E1 andreference electrode E01; capacitance element electrode E2 and referenceelectrode E02; capacitance element electrode E3 and reference electrodeE03; and capacitance element electrode E1 and reference electrode E01have the same central angle of the fan shape, and are formed so as tohave the same center.

FIG. 15 is a circuit diagram showing a signal processing circuit forX-axial component of the capacitance type sensor according to the firstmodification. The different point of the signal processing circuit ofFIG. 15 from the signal processing circuit of the capacitance typesensor of FIG. 1 is that the reference electrodes E01 and E02 on thesubstrate 20 are formed separately for the respective capacitanceelement electrodes E1 and E2. Therefore, the displacement electrode 40is grounded at separate positions through capacitance elements C01 andC02, respectively. The same applies to detection for a Y-axialcomponent.

When a plurality of reference electrodes E01 to E04 are thus dividedlyformed, even in the case that the capacitance element electrodes E1 toE4 are surrounded by the reference electrodes E01 to E04, wiring for thecapacitance element electrodes can easily be provided through theintervals between the reference electrodes E01 to E04. Although thereference electrode is divided into four in this modification, thenumber of divided reference electrodes and the shape and arrangement ofthe divided reference electrodes are arbitrary, and they can beadequately changed in consideration of the arrangement of wiring on thesubstrate.

Next, a second modification of the embodiment of the present inventionwill be described with reference to drawings. FIG. 16 is a circuitdiagram showing a signal processing circuit for X-axial component of thecapacitance type sensor, according to the second modification. Thesignal processing circuit of FIG. 16 differs from the signal processingcircuit of the capacitance type sensor of FIG. 1 on the points that: anopen collector type inverter element 91 is provided between the terminalT1 and the resistance element R1 and the capacitance element C1;likewise, an open collector type inverter element 92 is provided betweenthe terminal T2 and the resistance element R2 and the capacitanceelement C2; and the terminals of the resistance elements R1 and R2opposite to the terminals of the resistance elements R1 and R2 connectedto the terminals T1 and T2 are kept at a fixed potential Vcc. The otherconstruction is the same as that of the capacitance type sensor of FIG.1, and thus the same references are used for the other construction toomit the description thereof. The open collector type inverter elements91 and 92 are control elements each having a function of having noinfluence upon the input terminal of the corresponding EX-OR elementwhen the signal being input to the corresponding capacitance elementelectrode with periodically repeating high and low levels is at the highlevel; and discharging the capacitance element when the signal is at thelow level.

Changes in the potentials at the nodes X11 and X12 of the signalprocessing circuit shown in FIG. 10( b) and at the nodes X31 and X32 ofthe signal processing circuit shown in FIG. 16 when periodic signals arebeing input to the terminals T1 and T2 will be described with referenceto FIG. 17. Here, only the changes in the potentials at the nodes X11and X31 will be described.

As shown in FIG. 17, a case wherein a signal in which “Hi” and “Lo”signals are repeated is being input to the terminal T1 will bedescribed. After the input of an “Hi” signal starts, the potential atthe node X11 gradually rises because electric charges are graduallyaccumulated in the capacitance element C1 constituting a CR delaycircuit. After the input of a “Lo” signal starts, the potential at thenode X11 gradually lowers because electric charges are graduallyreleased from the capacitance element C1 constituting the CR delaycircuit. These changes are repeated. On the other hand, after the inputof an “Hi” signal starts, the potential at the node X31 gradually risesbecause electric charges are gradually accumulated in the capacitanceelement C1 constituting the CR delay circuit. After the input of a “Lo”signal starts, the potential at the node 31 lowers in a moment becauseelectric charges are released from the capacitance element C1constituting the CR delay circuit, in a moment through the opencollector type inverter element 91. These changes are repeated.

When the above-described construction is adopted and the duty ratio ofthe periodic signal being input to the terminal T1 is increased,charging each capacitance element can be efficiently performed becauseelectric charges are released from the capacitance element in a moment.Additionally, in the signal processing circuit of FIG. 16, the cycle ofthe periodic signal can be shortened in comparison with that of thesignal processing circuit of FIG. 10( b), and thereby the density ofwaveforms can be increased. Thus, the sensitivity of the signalprocessing circuit can be improved.

Next, a third modification of the embodiment of the present inventionwill be described with reference to a drawing. FIG. 18 is a circuitdiagram showing a signal processing circuit for X-axial component of thecapacitance type sensor, according to the third modification. The signalprocessing circuit of FIG. 18 differs from the signal processing circuitof the capacitance type sensor of FIG. 1 on the point that an OR elementis used as a logic element in place of the EX-OR element. The otherconstruction is the same as that of the capacitance type sensor of FIG.1, and thus the same references are used for the other construction toomit the description thereof.

In FIG. 18, the periodic signal A being input to the terminal T1 passesthrough the CR delay circuit constituted by the capacitance element C1and the resistance element R1, and then reaches the node X11. At thistime, the periodic signal at the node X11 has a predetermined delay, asshown in FIG. 12. Likewise, the periodic signal B being input to theterminal T12 passes through the CR delay circuit constituted by thecapacitance element C2 and the resistance element R2, and then reachesthe node X12. At this time, the periodic signal at the node X12 has apredetermined delay. Similarly to the case of FIG. 10( b), signals thatthe periodic signals at the nodes X11 and X12 have been converted bypassing through the Schmitt trigger type buffer elements 111 and 112 areinput to an OR element 134. An OR operation is performed between thosesignals, and the result of the operation is output to the terminal T11.In this case, the signal output to the terminal T11 is a rectangularwave signal having a predetermined duty ratio.

The quantity of the change in duty ratio of the rectangular wave signaloutput to the terminal T11 when the OR element 134 is used, from therectangular wave signal output to the terminal T11 when the detectivemember 30 is receiving no operation, is smaller than that of therectangular wave signal output to the terminal T11 when the EX-ORelement 131 is used. For this reason, the sensitivity characteristic ofthe capacitance type sensor may be lowered.

Therefore, this modification is preferably used for controlling thesensitivity characteristic of the capacitance type sensor, particularlylowering the sensitivity characteristic, by the construction of thesignal processing circuit in the case that each component of thecapacitance type sensor is made of a material that can make thesensitivity characteristic very good.

Next, a fourth modification of the embodiment of the present inventionwill be described with reference to a drawing. FIG. 19 is a circuitdiagram showing a signal processing circuit for X-axial component of thecapacitance type sensor, according to the fourth modification. Thesignal processing circuit of FIG. 19 differs from the signal processingcircuit of the capacitance type sensor of FIG. 1 on the point that anAND element is used as a logic element in place of the EX-OR element.The other construction is the same as that of the capacitance typesensor of FIG. 1, and thus the same references are used for the otherconstruction to omit the description thereof.

In FIG. 18, the periodic signal A being input to the terminal T1 passesthrough the CR delay circuit constituted by the capacitance element C1and the resistance element R1, and then reaches the node X11. At thistime, the periodic signal at the node X11 has a predetermined delay, asshown in FIG. 12. Likewise, the periodic signal B being input to theterminal T12 passes through the CR delay circuit constituted by thecapacitance element C2 and the resistance element R2, and then reachesthe node X12. At this time, the periodic signal at the node X12 has apredetermined delay. Similarly to the case of FIG. 10( b), signals thatthe periodic signals at the nodes X11 and X12 have been converted bypassing through the Schmitt trigger type buffer elements 111 and 112 areinput to an AND element 135. An AND operation is performed between thosesignals, and the result of the operation is output to the terminal T11.In this case, the signal output to the terminal T11 is a rectangularwave signal having a predetermined duty ratio.

The quantity of the change in duty ratio of the rectangular wave signaloutput to the terminal T11 when the AND element 135 is used, from therectangular wave signal output to the terminal T11 when the detectivemember 30 is receiving no operation, is smaller than that of therectangular wave signal output to the terminal T11 when the EX-ORelement 131 is used. For this reason, the sensitivity characteristic ofthe capacitance type sensor may be lowered.

Therefore, this modification is preferably used for controlling thesensitivity characteristic of the capacitance type sensor, particularlylowering the sensitivity characteristic, by the construction of thesignal processing circuit in the case that each component of thecapacitance type sensor is made of a material that can make thesensitivity characteristic very good.

Next, a fifth modification of the embodiment of the present inventionwill be described with reference to a drawing. FIG. 20 is a circuitdiagram showing a signal processing circuit for X-axial component of thecapacitance type sensor, according to the fifth modification. The signalprocessing circuit of FIG. 20 differs from the signal processing circuitof the capacitance type sensor of FIG. 1 on the point that a NANDelement is used as a logic element in place of the EX-OR element. Theother construction is the same as that of the capacitance type sensor ofFIG. 1, and thus the same references are used for the other constructionto omit the description thereof.

In FIG. 20, the periodic signal A being input to the terminal T1 passesthrough the CR delay circuit constituted by the capacitance element C1and the resistance element R1, and then reaches the node X11. At thistime, the periodic signal at the node X11 has a predetermined delay, asshown in FIG. 12. Likewise, the periodic signal B being input to theterminal T12 passes through the CR delay circuit constituted by thecapacitance element C2 and the resistance element R2, and then reachesthe node X12. At this time, the periodic signal at the node X12 has apredetermined delay. Similarly to the case of FIG. 10( b), signals thatthe periodic signals at the nodes X11 and X12 have been converted bypassing through the Schmitt trigger type buffer elements 111 and 112 areinput to a NAND element 136. A NAND operation is performed between thosesignals, and the result of the operation is output to the terminal T11.In this case, the signal output to the terminal T11 is a rectangularwave signal having a predetermined duty ratio.

The quantity of the change in duty ratio of the rectangular wave signaloutput to the terminal T11 when the NAND element 136 is used, from therectangular wave signal output to the terminal T11 when the detectivemember 30 is receiving no operation, is smaller than that of therectangular wave signal output to the terminal T11 when the EX-ORelement 131 is used. For this reason, the sensitivity characteristic ofthe capacitance type sensor may be lowered.

Therefore, this modification is preferably used for controlling thesensitivity characteristic of the capacitance type sensor, particularlylowering the sensitivity characteristic, by the construction of thesignal processing circuit in the case that each component of thecapacitance type sensor is made of a material that can make thesensitivity characteristic very good.

Next, a sixth modification of the embodiment of the present inventionwill be described with reference to a drawing. FIG. 21 is a circuitdiagram showing a signal processing circuit for X-axial component of thecapacitance type sensor, according to the sixth modification. The signalprocessing circuit of FIG. 21 differs from the signal processing circuitof the capacitance type sensor of FIG. 1 on the point that hysteresiscomparators 141 and 142 are used in place of the Schmitt trigger typebuffer elements 111 and 112. The other construction is the same as thatof the capacitance type sensor of FIG. 1, and thus the same referencesare used for the other construction to omit the description thereof.

The hysteresis comparators 141 and 142 are made up of comparators 141 aand 142 a, variable resistors Rf1 and Rf2, reference voltages 141 b and142 b, and resistance elements Rc1 and Rc2, respectively. Resistanceelements Rp1 and Rp2 as pull-up resistances are connected to the outputterminals of the respective comparators 141 a and 142 a. The terminalsof the resistance elements Rp1 and Rp2 opposite to the output terminalsof the resistance elements Rp1 and Rp2 are kept at a fixed potentialVcc.

One input terminal of the comparator 141 a is connected to the outputterminal of the resistance element Rc1, and the other input terminal isconnected to the reference voltage 141 b. Thus, a node X141 between thecomparator 141 a and the reference voltage 141 b is kept at apredetermined potential. A node between the one input terminal of thecomparator 141 a and the resistance element Rc1 is connected through thevariable resistor Rf1 to a node between the output terminal of thecomparator 141 a and an EX-OR element 131. The node between the outputterminal of the comparator 141 a and the EX-OR element 131 is connectedto the resistance element Rp1 so as to pull up the output of thecomparator 141 a. The hysteresis comparator 142 is the same as thehysteresis comparator 141 in construction, and thus the description ofthe construction of the hysteresis comparator 142 is omitted.

In the hysteresis comparator 141, there are below relations among thepower supply voltage Vcc, the positive threshold voltage Vp, thenegative threshold voltage Vn, and the hysteresis voltage Vht as thevoltage difference between Vp and Vn. In the below equations, theresistance value of the variable resistor Rf1 included in the hysteresiscomparator 141 is represented by Rf; the resistance value of theresistance element Rc1 is represented by Rc; and the voltage value ofthe reference voltage 141 b is represented by Vref. Also in thehysteresis comparator 142, there are the same relations.V _(p) =V _(ref)(R _(c) +R _(f))/R _(f)  Equation 1V _(n) ={V _(ref)(R _(c) +R _(f))−V _(cc) R _(c) }/R _(f)  Equation 2V _(ht) =V _(cc) R _(c) /R _(f)  Equation 3

For example, in the hysteresis comparator 141, when the power supplyvoltage Vcc, the voltage of the reference voltage 141 b, the resistancevalue Rc of the resistance element Rc1, and the resistance value Rf ofthe variable resistor Rf1 are 5 V, 2.5 V, 10 kilohm, and 100 kilohm,respectively, the positive threshold voltage Vp, the negative thresholdvoltage Vn, and the hysteresis voltage Vht are 2.75 V, 2.25 V, and 0.5V, respectively.

In this modification, the input voltages of the hysteresis comparators141 and 142 suffer conversion processing similar to that for the inputvoltages of the Schmitt trigger type buffer elements 111 and 112. Thatis, when the input voltage rises to more than the positive thresholdvoltage Vp, the output signal is changed over from a “Lo” signal to a“Hi” signal. On the other hand, when the input voltage lowers to lessthan the negative threshold voltage Vn, the output signal is changedover from a “Hi” signal to a “Lo” signal.

In FIG. 21, the periodic signal A being input to the terminal T1 passesthrough the CR delay circuit constituted by the capacitance element C1and the resistance element R1, and then reaches the node X11. At thistime, the periodic signal at the node X11 has a predetermined delay, asshown in FIG. 12. Likewise, the periodic signal B being input to theterminal T2 passes through the CR delay circuit constituted by thecapacitance element C2 and the resistance element R2, and then reachesthe node X12. At this time, the periodic signal at the node X12 has apredetermined delay. Thus, like the case of FIG. 10( b), rectangularwave signals converted from the periodic signals at the nodes X11 andX12 by passing through the respective hysteresis comparators 141 and 142are input to the EX-OR element 131, where an exclusive OR operation isperformed to those signals and the result of the operation is output tothe terminal T11. In this case, the signal output to the terminal T11 isa rectangular wave signal having a predetermined duty ratio.

As described above, to make the capacitance type sensor 10 of thisembodiment have hysteretic characteristics, a hysteresis comparator canbe used in place of using a Schmitt trigger type buffer element. In sucha hysteresis comparator, its hysteresis voltage Vht as the differencebetween its positive and negative threshold voltages Vp and Vn can bearbitrarily changed by changing the resistance value of a variableresistor constituting the hysteresis comparator, such as Rf1 or Rf2 inFIG. 21. Thus, the sensitivity characteristic of the capacitance typesensor can be easily controlled by the construction of its signalprocessing circuit.

Next, a seventh modification of the embodiment of the present inventionwill be described with reference to a drawing. FIG. 22 is a circuitdiagram showing a signal processing circuit for X-axial component of thecapacitance type sensor, according to the seventh modification. Thesignal processing circuit of FIG. 22 differs from the signal processingcircuit of the capacitance type sensor of FIG. 1 on the point that thedisplacement electrode 40 as one electrodes of the capacitance elementsC1 and C2 is directly grounded without connecting through thecapacitance element C0. The other construction is the same as that ofthe capacitance type sensor of FIG. 1, and thus the same references areused for the other construction to omit the description thereof.

The displacement electrode 40 is grounded through wiring providedseparately, and the reference electrode E0 need not be formed on thesubstrate 20. Therefore, wiring for the capacitance element electrodescan be easily provided on the substrate 20.

Although a preferred embodiment of the present invention has beendescribed, the present invention is not limited to the above-describedembodiment, and various changes in design can be made within the scopeof the description of claims. For example, in the above-describedembodiment, a signal processing circuit is used that has hystereticcharacteristics by utilizing a Schmitt trigger type logic element, aSchmitt trigger type buffer element, a Schmitt trigger type inverterelement, or a hysteresis comparator. However, the present invention isnot limited to this. Any construction of a signal processing circuit canbe used if it has hysteretic characteristics similar to those of theabove-described embodiment.

In the above-described embodiment, the displacement electrode isdisplaced relatively to the fixed capacitance element electrodes so asto change the capacitance values of the capacitance elements formedbetween the displacement electrode and the respective capacitanceelement electrodes. However, the present invention is not limited tothis. Any construction may be used for changing the capacitance value ofa capacitance element. For example, an insulating member may be movedbetween a fixed capacitance element electrode and a fixed conductivemember so as to change the capacitance value of the capacitance elementformed between the capacitance element electrode and the conductivemember.

In the above-described embodiment, the capacitance element electrodesare formed so as to correspond to three of X-, Y-, and Z-axes. However,capacitance element electrodes may be formed so as to be able to detectonly necessary axial components in accordance with application.

INDUSTRIAL APPLICABILITY

A capacitance type sensor of the present invention is most suitable foruse as an input device for a personal computer, a portable telephone, agame machine, or the like; a force sensor; an acceleration sensor; or apressure sensor.

1. A capacitance type sensor comprising: a substrate that provides an XYplane of an XYZ three-dimensional coordinate system; a detective memberbeing opposed to the substrate; a conductive member disposed between thesubstrate and the detective member so as to be Z-axially displaceable inaccordance with Z-axial displacement of the detective member; acapacitance element electrode formed on the substrate to cooperate withthe conductive member to form a first capacitance element; and areference electrode formed on the substrate to cooperate with theconductive member to form a second capacitance element, and kept at aground potential or another fixed potential, wherein the first andsecond capacitance elements are connected in series in relation to asignal input to the capacitance element electrode, and displacement ofthe detective member can be detected on the basis of detection of achange in the capacitance value of the first capacitance element causedby a change in the interval between the conductive member and thecapacitance element electrode; and wherein the capacitance type sensorcomprises two capacitance element electrodes in a pair, and after eachof analog signals corresponding to signals respectively input to acircuit including one of the capacitance element electrodes and acircuit including the other of the capacitance element electrodes, haspassed the respective signal processing circuit having hystereticcharacteristics and the analog signals are input to a logic element, anoutput signal is output from the logic element.
 2. The capacitance typesensor according to claim 1, wherein the capacitance element electrodeincludes a pair of first capacitance element electrodes disposedsymmetrically with respect to a Y axis, a pair of second capacitanceelement electrodes disposed symmetrically with respect to an X axis, anda third capacitance element electrode disposed near an origin.
 3. Thecapacitance type sensor according to claim 1, wherein a threshold valueof the signal processing circuit for an increasing input signal ishigher than a threshold value of the signal processing circuit for adecreasing input signal.
 4. The capacitance type sensor according toclaim 1, wherein a Schmitt trigger type buffer element is utilized inthe signal processing circuit.
 5. The capacitance type sensor accordingto claim 1, wherein a Schmitt trigger type inverter element is utilizedin the signal processing circuit.
 6. The capacitance type sensoraccording to claim 1, wherein a hysteresis comparator is utilized in thesignal processing circuit.
 7. The capacitance type sensor according toclaim 1, wherein a circuit including one of the capacitance elementelectrodes and a circuit including the other of the capacitance elementelectrodes are provided with a signal at a different phase of eachother.
 8. The capacitance type sensor according to claim 1, wherein thetime constant between a CR circuit including one of the capacitanceelement electrodes and a CR circuit including the other of thecapacitance element electrodes is different.
 9. The capacitance typesensor according to claim 1, wherein the signal periodically, repeatshigh-level and low-level, and a control element having a function ofdischarging the first capacitance element when the signal is at thelow-level is provided.
 10. The capacitance type sensor according toclaim 9, wherein an open collector type inverter element is used as thecontrol element.
 11. A capacitance type sensor comprising: a substratethat provides an XY plane of an XYZ three-dimensional coordinate system;a detective member being opposed to the substrate; a conductive memberdisposed between the substrate and the detective member so as to beZ-axially displaceable in accordance with Z-axial displacement of thedetective member; a capacitance element electrode formed on thesubstrate to cooperate with the conductive member to form a firstcapacitance element; and a reference electrode formed on the substrateto cooperate with the conductive member to form a second capacitanceelement, and kept at a ground potential or another fixed potential;wherein the first and second capacitance elements are connected inseries in relation to a signal input to the capacitance elementelectrode, and displacement of the detective member can be detected onthe basis of detection of a change in the capacitance value of the firstcapacitance element caused by a change in the interval between theconductive member and the capacitance element electrode; and wherein thesensor comprises two capacitance element electrodes in a pair, and eachof analog signals corresponding to signals respectively input to acircuit including one of the capacitance element electrodes and acircuit including the other of the capacitance element electrodes isinput to a Schmitt trigger type logic element having Schmitt triggerinput characteristics and an output signal is output from the Schmitttrigger type logic element.
 12. The capacitance type sensor according toclaim 11, wherein the capacitance element electrode includes a pair offirst capacitance element electrodes disposed symmetrically with respectto a Y axis, a pair of second capacitance element electrodes disposedsymmetrically with respect to an X axis, and a third capacitance elementelectrode disposed near an origin.
 13. The capacitance type sensoraccording to claim 11, wherein a threshold value of the signalprocessing circuit for an increasing input signal is higher than athreshold value of the signal processing circuit for a decreasing inputsignal.
 14. The capacitance type sensor according to claim 11, whereinthe Schmitt trigger type logic element implements the exclusive logicalOR operation.
 15. The capacitance type sensor according to claim 11,wherein the Schmitt trigger type logic element implements the logical ORoperation.
 16. The capacitance type sensor according to claim 11,wherein the Schmitt trigger type logic element implements the logicalAND operation.
 17. The capacitance type sensor according to claim 11,wherein the Schmitt trigger type logic element implements the logicalAND operation and the logical NOT operation.
 18. The capacitance typesensor according to claim 11, wherein a circuit including one of thecapacitance element electrodes and a circuit including the other of thecapacitance element electrodes are provided with a signal at a differentphase of each other.
 19. The capacitance type sensor according to claim11, wherein the time constant between a CR circuit including one of thecapacitance element electrodes and a CR circuit including the other ofthe capacitance element electrodes is different.
 20. The capacitancetype sensor according to claim 11, wherein the signal periodicallyrepeats high-level and low-level, and a control element having thefunction of discharging the first capacitance element when the signal isat a low-level is provided.
 21. The capacitance type sensor according toclaim 20, wherein an open collector type inverter element is used as thecontrolling element.